The invention concerns in any case synthetic fibres, such as plastic fibres and absorbent fibres, such as viscose and cellulose fibres to produce a fibre web, which at least include one heat-treatment section for heating up the synthetic fibres at least to one in advance determined temperature, and at least one hydro-entangling section with liquid nozzles to aim a number of powerful liquid jets against one made of synthetic fibres and absorbent fibres combined fibre layer.
A such plant is known, where long, carded, synthetic fibres of for instance polypropylene or polyethylene are laid in a web shaped layer on the top side of a net shaped, endless wire's upper tissue, which while running simultaneously runs in a direction, which points towards the plant's outlet. On the same or on a following wire the fibre layer hereafter is guided through an oven, where the fibres are heated up to such a high temperature that they will be tied together with cross bonds in the affected areas.
A thermal bonding fibre layer has now been formed, serving as a framework and supporting web for absorbent fibres, such as viscose and/or cellulose fibres, which as web can be un-winded from a roller or applied in an air-flow with the help of a known forming head.
A close-meshed wire transports hereafter the supporting web with the applicated fibres through a battery of water nozzles, which send a powerful water jets down against the fibres, which hereby are driven effectively into the underlying, frame-like supporting web.
When the water jets touch the close-meshed wire, part of the water is hit back against the supporting web, with the help of which the applicated fibres are wound around the cross bonded, synthetic fibres and are laid closely against the web's lower side, which hereby will be conveyed a smooth and flush surface.
The mentioned water exposure is in technical terms called hydro-entangling or spun-lacing. In the following the term hydro-entangling will be used.
The hydro-entangled web is dried in an oven, and finally the web is wound up in shape of a roller.
Fibre webs, which are manufactured in this way, are for instance used for products as wet wipes, towels, drapes, and gowns.
The above described process can be varied in several ways, which however has in common that they all start with a carded fibre layer. Typically the layers will be of polypropylene, polyethylene, or viscose, or a mixture of such fibres.
The carded made supporting web is soft and suitable for absorbing and intimately connect with the applicated fibres. In the longitudinal direction besides the web has such a matching strength that the process can proceed without a large risk of web breakage, which could lead to expensive stops of production and losses of materials.
Another advantage is that during the hydro-entangling process hydrogen bonds are made between the fibres, to avoid that the finished product flock and mote by use or processing.
The carding process however is slower than the following processes, which therefore cannot proceed with optimum capacity, this means the yield is reduced to a level, which is set by the carding process. Since plants of this kind are extremely expensive, it must be considered a serious lack that a great part of the known plant thus is not being used to the full extent.
Besides the carding process requiring close supervision and control, and it is difficult and complicated to work with, because for instance during running it is necessary to stretch the carded fibre layer.
The synthetic fibres, which make up the supporting web are furthermore considerably more expensive than cellulose fibres, and since the known process requires that approximately equal size quantities are being used of the two fibre types, the resulting product becomes expensive.
Even with the above mentioned content of synthetic fibres, the finished fibre web anyhow will suffer from the main lack that there exists an even big difference in the strength respectively in the longitudinal and transverse direction. The strength scale is typically 5:1. Products, which are manufactured of such fibre webs, therefore may tend to part alongside during use. Thus it is easy to stick a finger through the product.
A further disadvantage is that the known plant due to the carding process is rather unfit for production of sandwich webs, where the carded fibres become a part of several layers. The known plant can therefore not be used for production of one of today's strongly demanded products, which consists of two non-woven fibre layers with an intermediate air-laid fibre layer, which is tied together with the two others by the help of hydro-entangling layer, which is tied together with the two others by the help of hydro-entangling.